Methods and apparatus for operating gas turbine engines

ABSTRACT

A gas turbine engine assembly includes at least one propelling gas turbine engine and an auxiliary engine used for generating power. The propelling gas turbine engine includes a fan assembly and a core engine downstream from said fan assembly. The core engine includes a compressor, a high pressure turbine, a low pressure turbine, and a booster turbine coupled together in serial-flow arrangement such that the booster turbine is rotatably coupled between the high and low pressure turbines. The auxiliary engine includes at least one turbine and an inlet. The inlet is upstream from the high pressure turbine and is in flow communication with the propelling gas turbine engine core engine, such that a portion of airflow entering the propelling engine is extracted for use by the auxiliary engine.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/799,523 filed Mar. 12, 2004 now U.S. Pat. No. 7,121,078,which is a continuation-in-part of U.S. patent application Ser. No.10/352,446 filed Jan. 28, 2003 now U.S. Pat. No. 6,968,674, both ofwhich are assigned to assignee of the present invention, and both ofwhich are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

This invention relates generally to the gas turbine engines, and, moreparticularly, to methods and apparatus for operating gas turbine enginesused for aircraft propulsion and auxiliary power.

Gas turbine engines typically include a compressor for compressing air.The compressed air is mixed with a fuel and channeled to a combustor,wherein the fuel/air mixture is ignited within a combustion chamber togenerate hot combustion gases. The combustion gasses are channeled to aturbine, which extracts energy from the combustion gases for poweringthe compressor, as well as producing useful work. The exhaust gases arethen discharged through an exhaust nozzle, thus producing a reactive,propelling force.

Modern aircraft have increased hydraulic and electrical loads. Anelectrical load demanded of gas turbine engines increases as flightcomputers, communication equipment, navigation equipment, radars,environmental control systems, advanced weapon systems, and defensivesystems are coupled to aircraft. A hydraulic load demanded of gasturbine engines increases as flight controls, pumps, actuators, andother accessories are coupled to the aircraft. Within at least someknown aircraft, mechanical shaft power is used to power hydraulic pumps,electrical generators and alternators. More specifically, electrical andhydraulic equipment are typically coupled to an accessory gearbox thatis driven by a shaft coupled to the turbine. When additional electricalpower or hydraulic power is required, additional fuel is added to thecombustor until a predefined maximum temperature and/or power operatinglevel is reached.

Because the density of air decreases as the altitude is increased, whenthe aircraft is operated at higher altitudes, the engine must workharder to produce the same shaft power that the engine is capable ofproducing at lower altitudes. As a result of the increased work, theturbine may operate with increased operating temperatures, such that theshaft power must be limited or reduced to prevent exceeding the enginepredefined operating limits.

Within at least some known gas turbine engines, electrical power andhydraulic power is also generated by an auxiliary power unit (APU). AnAPU is a small turbo-shaft engine that is operated independently fromthe gas turbine engines that supply thrust for the aircraft. Morespecifically, because APU operation is also impacted by the air densityand is also operationally limited by predefined temperature andperformance limits, APUs are typically only operated when the aircraftis on the ground, or in emergency situations while the aircraft is inflight.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, a method for assembling a gas turbine engine assembly isprovided. The method comprises providing at least one propelling gasturbine engine that includes a core engine including a compressor, ahigh pressure turbine, and a booster turbine coupled together inserial-flow arrangement, and coupling an auxiliary engine to thepropelling gas turbine engine such that during operation of thepropelling gas turbine engine, at least a portion of the airflowentering the propelling gas turbine engine is selectively extracted fromthe propelling gas turbine engine upstream from the core engine highpressure turbine, and channeled to the auxiliary engine for generatingpower.

In another aspect, a gas turbine engine assembly is provided. The gasturbine engine assembly includes at least one propelling gas turbineengine and an auxiliary engine used for generating power. The propellinggas turbine engine includes a fan assembly and a core engine downstreamfrom said fan assembly. The core engine includes a compressor, a highpressure turbine, a low pressure turbine, and a booster turbine coupledtogether in serial-flow arrangement such that the booster turbine isrotatably coupled between the high and low pressure turbines. Theauxiliary engine includes at least one turbine and an inlet. The inletis upstream from the booster turbine and is in flow communication withthe propelling gas turbine engine core engine, such that a portion ofairflow entering the propelling engine is extracted for use by theauxiliary engine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary schematic view of a gas turbine engine assembly;and

FIG. 2 is an exemplary schematic view of an alternative embodiment of agas turbine engine assembly.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is an exemplary schematic view of a gas turbine engine assembly10 including a propelling gas turbine engine 11 and an auxiliary powerunit or auxiliary power engine 12 that are coupled together, asdescribed in more detail below, in a combined cycle. More specifically,gas turbine engine assembly 10, as described in more detail below,facilitates producing shaft power and propelling force for an aircraft(not shown).

Gas turbine engine 11 includes a core engine 13 and a fan assembly 14and a low pressure turbine assembly 16. Fan assembly 14 and low pressureturbine 16 are coupled by a first shaft 18. Core engine 13 includes acore drive fan 20, a high-pressure compressor 22, a combustor (notshown), and a high-pressure turbine 24. In the exemplary embodiment,core drive fan 20, compressor 22, the combustor, and turbines 24 and 16are coupled together in axial flow communication. Core drive fan 20,compressor 22, and high pressure turbine 24 are coupled by a secondshaft 28. Gas turbine engine 11 also includes an inlet side 32 and anexhaust side 34. In one embodiment, engine 11 is a F118-GE-100 turbofanengine commercially available from General Electric Aircraft Engines,Cincinnati, Ohio.

In operation, inlet air, represented by arrow 40, enters fan assembly14, wherein the air is compressed and is discharged downstream,represented by arrow 41, at an increased pressure and temperaturetowards core engine 13 and more specifically, towards core drive fan 20wherein the air is channeled towards compressor 22. In one embodiment,engine 11 includes a bypass duct (not shown), such that a portion of air41 discharged from fan assembly 14 is channeled into the bypass ductrather than entering core engine 11.

Highly compressed air 45 from compressor 22 is delivered to thecombustor wherein it is mixed with fuel and ignited. Combustion gasespropel turbines 24 and 16, which drive compressor 22, core drive fan 20,and fan assembly 14, respectively. In the exemplary embodiment, coreengine exhaust 44 is discharged from engine 11 to generate a propellingforce from gas turbine engine assembly 10.

In the exemplary embodiment, core engine exhaust 44 is channeled to avariable area bypass injector 50 that is coupled in flow communicationwith core engine exhaust 44 and engine exhaust 52 discharged from orauxiliary power engine 12. In an alternative embodiment, core engineexhaust 44 is channeled to a mixing damper (not shown) that is coupledin flow communication with core engine exhaust 44. In anotheralternative embodiment, core engine exhaust flow 44 and fan air aredischarged separately from auxiliary engine exhaust 52 to producethrust.

Auxiliary power engine 12 is coupled in flow communication to engine 11,as described in more detail below, and includes a compressor 60, ahigh-pressure turbine 62, and a low-pressure turbine 64. Compressor 60and high-pressure turbine 62 are connected by a first shaft 66, suchthat as combustion gases propel turbine 62, turbine 62 drives compressor60. Auxiliary engine 12 also includes a second shaft 68 that is coupledto low-pressure turbine 64 to provide shaft power output, represented byarrow 70, for use in the aircraft. For example, power output 70 may beused to drive equipment, such as, but not limited to alternators,generators, and/or hydraulic pumps. In one embodiment, auxiliary powerengine 12 is a turbo-shaft engine, such as a T700-GE-701 engine that iscommercially available from General Electric Company, Cincinnati, Ohio,and that has been modified in accordance with the present invention.

Auxiliary ducting (not shown) couples auxiliary power engine 12 toengine 11 to enable a portion of compressed air 41 channeled towardscore engine 13 to be directed to auxiliary power engine 12. Morespecifically, in the exemplary embodiment, auxiliary airflow,represented by arrow 80 is extracted from core engine 13 at a locationupstream from core engine turbine 24. Moreover, in the exemplaryembodiment, airflow 80 is bled from high-pressure compressor 22 and isrouted towards auxiliary engine compressor 60. In an alternativeembodiment, auxiliary power engine 12 is coupled in flow communicationto a pair of engines 11 and receives high pressure airflow 80 from eachengine 11. In another alternative embodiment, a pair of auxiliary powerengines 12 are coupled in flow communication to a single engine 11 andboth receive high pressure airflow 80 from engine 11. More specifically,in the exemplary embodiment, compressor 22 is a multi-staged compressorand air 80 may be extracted at any compressor stage within compressor 22based on pressure, temperature, and flow requirements of auxiliaryengine 12.

In another embodiment, air 80 is extracted upstream or downstream fromcompressor 22 from any of, or any combination of, but is not limited tobeing extracted from, a booster interstage, a booster discharge, a faninterstage, a fan discharge, a compressor inlet, a compressorinterstage, or a compressor discharge bleed port. In a furtheralternative embodiment, air 80 is extracted upstream from compressor 22.In one embodiment, approximately up to 10%, or more, of air flowing intocompressor 22 is extracted for use by auxiliary engine 12. In a furtherembodiment, approximately up to 10% or more, of air flowing into fanassembly 14 is extracted for used by auxiliary engine 12. In anotherembodiment, air is extracted from any of, or any combination of, but isnot limited to being extracted from, a location intermediate, orbetween, fan assembly 14 and core drive fan 20, core drive fan 20 andcompressor 22, and compressor 22 and turbine 24.

In an alternative embodiment, engine 11 supplies pressurized orcompressed air to auxiliary power engine 12. For example, in oneembodiment, compressed air supplied to an aircraft cabin is routed toauxiliary power engine 12 after being used within the aircraftenvironmental control system. In a further embodiment, auxiliary powerengine 12 receives a mixture of airflow from engine 11 and ambientairflow.

Auxiliary airflow 80 directed towards auxiliary engine 12 is at a higherpressure and temperature than inlet airflow 40 entering gas turbineengine assembly 10. Moreover, because auxiliary airflow 80 is at anincreased pressure and temperature than the pressure and temperature ofairflow 40 entering gas turbine engine assembly 10, a density of airflow80 is substantially similar to the density of airflow that entersauxiliary engine 12 at lower altitudes. Accordingly, because the poweroutput of auxiliary engine 12 is proportional to the density of theinlet air, during operation of core engine 11, auxiliary engine 12 isoperable at higher altitudes with substantially the same operating andperformance characteristics that are available at lower altitudes byauxiliary engine 12. For example, when used with the F110/F118 family ofengines, auxiliary engine 12 produces approximately the same horsepowerand operating characteristics at an altitude of 30-40,000 feet, as wouldbe obtainable if auxiliary engine 12 was operating at sea levelindependently. Accordingly, at mission altitude, a relatively smallamount of high-pressure air taken from core engine 11 will enableauxiliary power engine 12 to output power levels similar to thosesimilar from auxiliary power engine 12 at sea level operation.

In the exemplary embodiment, auxiliary airflow 80 is channeled throughan intercooler 90 prior to being supplied to auxiliary engine compressor60. Intercooler 90 has two airflows (not shown) flowing therethrough inthermal communication with each other, and accordingly, intercooler 90is designed to exchange a substantial amount of energy as heat, withminimum pressure losses. In the exemplary embodiment, auxiliary airflow80 is the heat source and a second airflow is used as a heat sink. Inone embodiment, the second airflow is fan discharge airflow. In anotherembodiment, the second airflow is ambient airflow routed through anengine nacelle and passing through intercooler 90 prior to beingdischarged overboard. More specifically, the operating temperature ofauxiliary airflow 80 is facilitated to be reduced within intercooler 90as the transfer of heat increases the temperature of the other airflowchanneled through intercooler 90. In an alternative embodiment, turbineengine assembly 10 does not include intercooler 90.

Intercooler 90 facilitates increasing an amount of power per pound ofbleed air 80 supplied to auxiliary power engine 12 without increasingflow rates or changing existing turbine hardware. A control system 92 iscoupled to a generator control system (not shown) and facilitatesregulating the operating speed of auxiliary power engine 12. In oneembodiment, control system 92 throttles inlet air 80 supplied to engine12 by control of a variable flow area throttle valve 94 and/or controlsengine backpressure by control of a variable flow area exit nozzle 96 ora variable area bypass injector 50 to facilitate controlling theoperation of auxiliary power engine 12.

Exhaust airflow 52 from auxiliary power engine 12 is channeled towardscore engine exhaust 44 at a discharge pressure that is substantially thesame as the discharge pressure of exhaust flow 44 discharged from coreengine 13. Specifically, in the exemplary embodiment, auxiliary engineexhaust airflow 52 is routed through variable area bypass injector 50which facilitates mixing exhaust flow 44 exiting core engine 13 withauxiliary engine exhaust airflow 52. More specifically, in the exemplaryembodiment, exhaust airflow 52 is reintroduced to core engine exhaustflow 44 upstream from a propelling core engine nozzle (not shown). Themixed exhaust flow 98 is then discharged through an engine nozzle (notshown). In an alternative embodiment, exhaust airflow 52 is not mixedwith core engine exhaust flow 44, but rather is discharged to ambientindependently from exhaust flow 44.

Accordingly, when operated, auxiliary power engine 12 facilitatesproviding increased shaft power production for use within the aircraft.More specifically, because auxiliary power engine 12 is selectivelyoperable for shaft power production, auxiliary power engine 12 may beused only when needed, thus facilitating fuel conservation for theaircraft. In addition, the design of gas turbine assembly 10 enablesauxiliary power engine 12 to be operated independently of propellingengine 11, such that an operating speed auxiliary power engine 12 isindependent of an operating speed of core engine 11. As such, auxiliarypower engine 12 may operated during non-operational periods of coreengine 11, and moreover, may be used to provide power necessary to startoperation of engine 11.

Operation of auxiliary power engine 12 facilitates improving surgemargin of engine 11 by bleeding airflow 80 as needed, such thataltitude, installation, or distortion effects may be overcome. Moreover,by removing high pressure extraction, auxiliary power engine 12 alsofacilitates improving an operating performance of core engine 11 whilegenerating significant power. Additionally the hydro mechanical ordigital controls of propelling engine 11 and auxiliary power engine 12are arranged to mutually exchange operational status and performanceparameter values (pressure, temperature, RPM, etc) from one to theother.

FIG. 2 is an exemplary schematic view of an alternative embodiment of agas turbine engine assembly 100 including a propelling gas turbineengine 11 and an auxiliary power unit or auxiliary power engine 12 thatare coupled together, as described in more detail below, in a combinedcycle. Engine 100 is substantially similar to engine 10 shown in FIG. 1and components in engine 100 that are identical to components of engine10 are identified in FIG. 2 using the same reference numerals used inFIG. 1. Similarly to gas turbine engine assembly 10, gas turbine engine100, as described in more detail below, facilitates producing shaftpower and propelling force for an aircraft (not shown).

Gas turbine engine 11 includes core engine 13, fan assembly 14, lowpressure turbine assembly 16, a booster fan 102, and a booster turbine104. Fan assembly 14 and low pressure turbine 16 are coupled by firstshaft 18. Booster fan 102 and booster turbine 104 are coupled togetherby a second shaft 110, and compressor 22 and high pressure turbine 24are coupled by a third shaft 112. Core engine 13 includes core drive fan20, high-pressure compressor 22, a combustor (not shown), andhigh-pressure turbine 24. In the exemplary embodiment, booster fan 102,compressor 22, the combustor, and turbines 24, 26, and 16 are coupledtogether in axial flow communication. Gas turbine engine 11 alsoincludes an inlet side 32 and an exhaust side 34.

In operation, inlet air, represented by arrow 40, enters fan assembly14, wherein the air is compressed and is discharged downstream,represented by arrow 41, at an increased pressure and temperaturetowards core engine 13 and more specifically, towards booster fan 102wherein the air is channeled towards compressor 22. In one embodiment,engine 11 includes a bypass duct (not shown), such that a portion of air41 discharged from fan assembly 14 is channeled into the bypass ductrather than entering core engine 11.

Auxiliary power engine 12 is coupled in flow communication to engine 102via auxiliary ducting (not shown) such that a portion of compressed air41 channeled towards core engine 13 may be directed to auxiliary powerengine 12. More specifically, in the exemplary embodiment, auxiliaryairflow 80 is extracted from core engine 13 at a location upstream fromcore engine turbine 24. Moreover, in the exemplary embodiment, airflow80 is bled from high-pressure compressor 22 and is routed towardsauxiliary engine compressor 60. In an alternative embodiment, auxiliarypower engine 12 is coupled in flow communication to a pair of engines100 and receives high pressure airflow 80 from each engine 100. Inanother alternative embodiment, a pair of auxiliary power engines 12 arecoupled in flow communication to a single engine 100 and both receivehigh pressure airflow 80 from engine 100. More specifically, in theexemplary embodiment, compressor 22 is a multi-staged compressor and air80 may be extracted at any compressor stage within compressor 22 basedon pressure, temperature, and flow requirements of auxiliary engine 12.

In another embodiment, air 80 is extracted upstream or downstream fromcompressor 22 from any of, or any combination of, but is not limited tobeing extracted from, a booster interstage, a booster discharge, a faninterstage, a fan discharge, a compressor inlet, a compressorinterstage, or a compressor discharge bleed port. In a furtheralternative embodiment, air 80 is extracted upstream from compressor 22.In another embodiment, air is extracted from any of, or any combinationof, but is not limited to being extracted from, a location intermediatefan assembly 14 and booster fan 102, intermediate booster fan 102 andcompressor 22, and intermediate compressor 22 and turbine 24. Referringto FIG. 2, “A”, “B”, and “C” represent exemplary locations from whichair may be extracted from core engine (13) for use by auxiliary powerengine (12).

The above-described power system is cost-effective and increases shaftpower production. The power system includes an auxiliary turbine enginecoupled in flow communication with a gas turbine engine including abooster turbine, such that inlet air provided to the auxiliary turbineis drawn from air flowing through the core engine. As such, higherdensity air is provided to the auxiliary engine than would be providedhad the auxiliary engine received ambient inlet airflow throughconventional means, such as through normally aspired means. Accordingly,a small amount of high-pressure air taken from the main engine willenable a smaller engine to output power levels similar to those of sealevel operation. As a result, the increased density of air facilitatesincreased shaft turbine power production from the auxiliary engine in acost-effective and reliable manner.

Exemplary embodiments of gas turbine assemblies are described above indetail. The assemblies are not limited to the specific embodimentsdescribed herein, but rather, components of each assembly may beutilized independently and separately from other components describedherein. For example, each turbine component and/or auxiliary turbineengine component can also be used in combination with other core engineand auxiliary turbine engine components.

While the invention has been described in terms of various specificembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theclaims.

1. A method for assembling a gas turbine engine assembly, said methodcomprising: providing at least one propelling gas turbine engine thatincludes a fan assembly and a core engine including a core drive fan, ahigh pressure compressor, and a high pressure turbine coupled togetherin serial-flow arrangement; and coupling an auxiliary engine to thepropelling gas turbine engine such that during operation of thepropelling gas turbine engine, at least a portion of the airflowentering the propelling gas turbine engine is selectively extracted fromat least one of the core drive fan and the high pressure compressor, andchanneled to the auxiliary engine for generating power, wherein theauxiliary engine includes an inlet, a compressor, and at least oneturbine.
 2. A method in accordance with claim 1 wherein coupling anauxiliary engine to the propelling gas turbine engine further comprisescoupling the auxiliary engine to the propelling gas turbine engine suchthat during operation of the propelling gas turbine engine, airflow isselectively extracted from the propelling gas turbine engine upstreamfrom the high pressure turbine and is channeled to the auxiliary engineat a higher pressure than a pressure of the airflow entering thepropelling gas turbine engine.
 3. A method in accordance with claim 1wherein coupling an auxiliary engine to the propelling gas turbineengine further comprises coupling the auxiliary engine to the propellinggas turbine engine such that during operation of the propelling gasturbine engine, airflow is extracted from at least one interstagelocation of the compressor between an inlet and a discharge of thecompressor.
 4. A method in accordance with claim 1 wherein providing atleast one propelling gas turbine engine further comprises providing thecore drive fan upstream from the core engine high pressure compressorand rotatably coupled to the high pressure turbine.
 5. A method inaccordance with claim 1 further comprising coupling a control system tothe auxiliary engine, the control system including at least oneadjustable air throttle valve to the auxiliary engine to selectivelycontrol extraction of air from the propelling engine.
 6. A gas turbineengine assembly comprising: at least one propelling gas turbine enginecomprising a fan assembly and a core engine assembly downstream fromsaid fan assembly, said core engine comprising a core drive fan, a highpressure compressor, and a high pressure turbine assembly coupledtogether in serial-flow arrangement; and an auxiliary engine used forgenerating power, said auxiliary engine comprising at least one turbineand an inlet, said inlet coupled upstream from said turbine and in flowcommunication with said propelling gas turbine engine core engine, suchthat a portion of airflow entering said at least one propelling gasturbine engine is extracted from at least one of the core drive fan andthe high pressure compressor, for use by said auxiliary engine.
 7. A gasturbine engine assembly in accordance with claim 6 wherein saidauxiliary engine receives air that has been extracted from said at leastone propelling gas turbine engine upstream from said core engine highpressure turbine assembly.
 8. A gas turbine engine assembly inaccordance with claim 6 wherein said auxiliary engine receives airflowextracted from at least one of an interstage of said compressor and adischarge of said compressor.